Stacks of loading coils find extensive use in the telephone industry where the individual coils are connected to wire pairs to balance the capacitance effect of these wires which are used as transmission lines from a central telephone office to a subscriber's telephone.
A number of expedients have been devised and used to package several loading coils in a container; for example, see U.S. Pat. No. 2,147,245 for a disclosure of a metal tube-like container; U.S. Pat. No. 2,548,205 for a disclosure of a cardboard tube container for receiving a single stack of coils, and U.S. Pat. No. 2,692,302 for a disclosure of a metal screen container tube. British Pat. No. 366,791 shows a cast iron case into which a plurality of cylindrical containers of loading coils are suspended.
There still is a need for a compact lightweight loading coil assemblage which can be used alone or with a number of similar assemblages to provide the necessary inductance to balance capacitance between transmission lines installed in the field.
These coil assemblages, which may be termed coil cases or coil packs, should permit easy assembly in the factory. Further, the coil case should permit assembly in the field of a number of other similar cases within an outer casing which receives encapsulant to provide electrical isolation between the coil packs, and further insure protection from rough handling and environmental attack. These coil packs should be compactly assembled with isolators and encapsulant to assure electrical isolation between each coil in each stack, and isolation between a pair of stacks mounted within a single case.